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Interactive: Hurricane Tracker

MIAMI — Tropical Storm Irene formed east of the Leeward Islands on Saturday and was expected to become a hurricane in the next two days heading on a northwestward track through the Caribbean that may threaten Florida.

Irene formed as Tropical Storm Harvey made landfall over Belize and weakened as it brought heavy rain to parts of Guatemala and eastern Mexico.

At 11 p.m., Irene, the ninth named storm of the 2011 Atlantic hurricane season, was packing winds of 50 miles per hour and was about 95 miles east of Dominica, approaching the Leeward Islands, the U.S.-based National Hurricane Center said.

Tropical storm warnings were issued for many of the Leeward Islands, the Virgin Islands and Puerto Rico, the center said after a U.S. Air Force Reserve "hurricane hunter" aircraft investigated the storm.

"Some strengthening is forecast during the next 48 hours and Irene could become a hurricane on Monday," the center said.

Forecasters said Irene would pass through the Leeward Islands early Sunday and then move into the northeastern Caribbean Sea. It is expected Sunday afternoon to bring tropical storm conditions, including 4 inches to 7 inches of rain, to Puerto Rico and the Virgin Islands. Hurricane conditions could occur in the Dominican Republic late Monday.

It would be the first hurricane of the so far busy, but to date not destructive, 2011 Atlantic hurricane season.

Computer forecast models showed Irene taking a northwestward path over Haiti and eastern and central Cuba and then heading up the western side of the Florida peninsula.

Depending on its eventual path and possible turns, Irene might still pose a threat to U.S. oil and gas installations in the Gulf of Mexico, but forecasters say this is too early to predict with certitude.

The NHC said that if Irene avoided land and stayed over warm Caribbean waters, conditions would be favorable for its strengthening. "Almost all the guidance shows Irene becoming a hurricane in a day or two," it added.

Tropical Storm Harvey made landfall on the coast of Central America earlier on Saturday, lashing Belize with strong winds and rain.

At 11 p.m. ET, the U.S. National Hurricane Center in Miami said Harvey was centered about 65 miles north-northwest of Tikal, Guatemala, moving west at 14 mph. Maximum sustained winds were 40 mph, down from 60 mph when it made landfall.

Forecasters say the storm's center will continue to move across northern Guatemala Saturday night and into eastern Mexico on Sunday.

The storm is expected to bring as much as 6 inches of rain to parts of Honduras, Guatemala, Belize and Mexico's Yucatan Peninsula. Forecasters say flash floods and mudslides are possible. It is expected to weaken to a tropical depression Sunday.

Mudslides and flooding could affect agricultural output in Central America, but this year's coffee and sugar harvests are largely over.

Harvey was expected to weaken to a tropical depression on Sunday, the NHC said.

Forecasters said Caribbean island states, the Bahamas and Florida needed to closely monitor the path of Irene.

"Given the uncertainties, this weekend would be a good time to go over your hurricane preparedness if you live anywhere in the Caribbean, Bahamas, or Florida, since (it) could well be paying you a visit as a tropical storm or hurricane sometime in the next week," hurricane expert Jeff Masters of private forecaster Weather Underground wrote in his blog on Saturday.

This article includes reporting from Reuters and The Associated Press.